1. Field of the Invention
This invention relates to a chlorine ion-selective electrode employable for quantitative analysis of chlorine ion contained in a liquid sample such as a body fluid.
2. Description of the Prior Art
There are known chlorine ion-selective electrodes comprising a silver metal layer, a silver chloride layer and a chlorine ion-selective membrane, superposed in this order, wherein said chlorine ion-selective membrane contains a hydrophobic organic polymer as a binder. For instance, such chlorine ion-selective electrodes are disclosed in U.S. Pat. No. 3,591,482.
Generally, the chlorine ion-selective membrane comprises a quaternary ammonium salt (e.g., Aliquat 336, tradename, manufactured by Aldrich Chemical, Inc.) and a hydrophobic organic polymer as a binder. As the hydrophobic organic polymer to be used as the binder in the ion-selective membrane, there are known, for instance, vinyl chloride copolymers described in Japanese Patent Provisional Publication No. 58(1983)-156848. However, the vinyl chloride copolymers have disadvantages in that they suffer greatly drift at the initial stage in the measurement of potential and further suffer the interference of co-existing bromine ion. Polyvinyl chlorides proposed as the binder prior to the above-described publication have similar disadvantages. When the drift at the initial stage in the measurement of potential is large, there is caused a problem that the reproducibility of potential to be measured after the lapse of a certain period after the contact of a liquid sample with the electrode becomes poor and hence, reproducibility of the analysis of the chlorine ion concentration becomes poor.